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Earthquakes/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby There is rumbling, and the ground shakes. Tim and Moby are in their house. Moby is standing at the bottom of the staircase. Tim rushes to him from upstairs. TIM: Did you feel that? MOBY: Beep. Moby shakes his head "no". TIM: No? Moby shrugs. He hands Tim a sheet of paper. Tim reads from a typed letter. TIM: Dear Tim and Moby, why do earthquakes happen? From, Daniel. Hi, Daniel. Here on the surface of the earth, things are usually pretty calm and stable. So you might think our planet is just a big, dead rock. But along with volcanoes, earthquakes are a powerful reminder that we're living on top of a fiery ball, protected only by a thin shell. This rigid outer layer is called the lithosphere, which means "ball of rock". An animation shows that, very far beneath Tim and Moby, the center of Earth is hot and molten. The animation zooms out to show the rigid outer layer, the lithosphere. TIM: But the ball isn't solid. It's a hollow, cracked shell. Each piece of this planetary jigsaw puzzle is called a tectonic plate. A world map shows the major cracks that exist in the lithosphere. They divide Earth's surface into several pieces. MOBY: Beep. TIM: Well, beneath the plates is a layer called the mantle. And farther in you have the core, which is about as hot as the surface of the Sun. An image shows Earth's layers as Tim describes them. TIM: That's easily enough to melt the mantle, but the weight of the lithosphere keeps it sort of half-solid, like clay. An animation of Earth's layers illustrates the weight of the lithosphere pressing on the mantle. TIM: Driven by the core's heat, the mantle slowly churns in movements called convection currents. Over millions of years, hot material rises away from the core, cools off, and sinks again. An animation shows the rotation of convection currents in the mantle. There are areas that are almost circular, one next to the other, that rotate. TIM: Since the plates are floating above, they get dragged along for the ride. An animation shows two tectonic plates moving away from each other because of the mantle's convection current activity beneath them. MOBY: Beep. TIM: No, you can't usually feel the movement. It's really slow, generally about a couple of inches a year. But it's an unstoppable motion, and in some places, it breaks the earth's crust into long faults. These cracks are the most common near plate boundaries. In some places, the slabs of rock on each side of a fault move smoothly. Animations illustrate how forces from different directions can create different kinds of faults. TIM: But in others, the slabs get stuck while the mantle below keeps moving. So a whole lot of pressure can build up over many years. One of the animations illustrates what Tim describes. The mantle beneath the two slabs churns as the slabs remain still. TIM: Eventually, the crust shifts, releasing an enormous amount of energy. MOBY: Beep. TIM: Yep, that release is called an earthquake. The energy moves outward from the hypocenter, the spot on the fault where the pressure first releases. An animation shows a hypocenter forming at a point along the fault where the two slabs meet. TIM: The spot on the earth's surface directly above the hypocenter is called the epicenter. The animation shows the location of the epicenter. It is directly above the hypocenter, as Tim describes. TIM: Now, believe it or not, hundreds of thousands of tiny earthquakes happen every year. They're just so small that people can't really feel them. An animated world map illustrates the locations of several small earthquakes. Most are near the coasts along the Pacific Ocean. TIM: But sometimes, a tremendous amount of energy is released. MOBY: Beep. TIM: The energy travels through the ground in the form of seismic waves. Some of these waves push straight outward, creating an explosive thud. An animation shows seismic waves traveling upward in a semicircle from beneath Earth's surface. The waves shake houses and trees in a quick, jiggling motion. TIM: Since these waves are the fastest, that's the first thing you feel during an earthquake. After that, you'll feel a rocking motion, as slower waves move material up and down. These kinds of waves create ripples on the surface, like a rock tossed into a pond. The animation shows the wavelike movement of ground beneath the houses and trees, rocking the surface as Tim describes. TIM: That's why the most intense shaking comes at the end of an earthquake. The surface waves rock buildings and other structures back and forth on their foundations. If the building materials aren't strong enough, they can collapse or fall over. The animation shows a house cracking and a tree falling over as a result of the surface waves. TIM: And even after those waves pass, places that have been shaken up still have to worry about aftershocks. Those are unpredictable earthquakes that occur shortly after big seismic events. An animation shows aftershocks shaking the houses and a piece breaking off one of the houses. TIM: They can be pretty strong and wreck buildings that have been damaged by the first quake. MOBY: Beep. TIM: Quakes are measured and recorded using a machine called a seismograph. A seismogram shows us how big the waves were and how long they lasted. An animation shows a simple seismograph at work. It is creating a seismogram by drawing a jagged line on a piece of paper. TIM: And the intensity of an earthquake is measured on the Moment Magnitude Scale. It runs from one to ten. Each number represents an earthquake ten times stronger than the one below it. An image shows the Moment Magnitude Scale. It is a vertical number line that runs from one point zero to ten point zero. TIM: So an earthquake that measures 4.0 is ten times more powerful than a 3.0 earthquake. Major earthquakes tend to measure 7.0 or higher. Arrows and shaded areas appear on the Moment Magnitude Scale to illustrate what Tim is describing. TIM: In 1906, an 8.0 earthquake basically wiped out the city of San Francisco. An image shows a reading of eight point zero on the Moment Magnitude Scale. A second image shows San Francisco in ruins. MOBY: Beep. TIM: That's true. California is on the Ring of Fire, a region of frequent seismic activity. A world map illustrates the Ring of Fire that Tim describes. It basically surrounds the Pacific Ocean. TIM: The plates in this area are constantly grinding against one another, fueling volcanoes and earthquakes. The boundaries of Earth's tectonic plates appear on the world map. The boundaries of several plates appear along the Ring of Fire. TIM: Many of these happen underwater, which can create an incredibly destructive wave called a tsunami. During a tsunami, waves up to one hundred feet high can destroy shorelines for thousands of miles. An animation shows seismic waves forming a tsunami beneath the ocean's surface. The tsunami hits shore, carrying off houses and trees. TIM: And that's what happened in two thousand four, when a nine point two earthquake rocked the Indian Ocean. An image shows people running from a tsunami that is hitting the ocean's shore. MOBY: Beep. TIM: Well, there's rarely any warning before an earthquake hits. But if you live in an area that's prone to earthquakes, like the West Coast of the United States, you should probably take a few precautions. Create a "ready kit" of essential supplies in case you need to evacuate quickly. An image shows a first-aid kit, a flashlight, toilet paper, a radio, bottled water, batteries, and other items that would be needed in an emergency situation. TIM: And plan how you and the rest of your family will contact each other. If there's a strong earthquake, get to a safe place inside your house, like against an interior wall, or under a sturdy table or desk. Be sure to hold on. An animation shows a girl taking shelter beneath a table. The house is shaking around her. She is holding on to a table leg. There is another rumbling at Tim and Moby's house. TIM: Don't tell me you didn't feel that? Moby is frightened. He takes Tim by the hand. They get under a table. Moby hugs Tim very tightly. TIM: I get why we're under the table, but why are you squeezing me? MOBY: Beep. Category:BrainPOP Transcripts